Two approaches for depositing ionized metals include direct current physical vapor deposition (DC PVD) and radio frequency (RF) PVD. The DC PVD process is characterized by a spacing between a substrate support surface of a substrate support and an opposing target containing material to be deposited on a substrate supported by the substrate support of about 190 to about 400 mm, referred to herein as tall spacing. The DC PVD process further uses a small unbalanced magnetron in a closed loop and operates at a relatively low pressure and high power. The combination of small magnetron and high DC power generates a large power density to ionize the gas medium and sputter the target. The low pressure and tall spacing provide a ‘ballistic’ transport mechanism where sputter material can reach the wafer with few if any in-flight collisions. Additional neutral metal is mainly deposited on the shields due to cosine type distribution and the tall spacing.
However, the inventors have observed that the small strong magnetron has a large drawback of localized sputtering. This localized sputtering will quickly erode at certain locations due to the electron confinement and localized gas ionization. This effect is further accelerated when magnetic materials such as cobalt (Co) and nickel (Ni) and their alloys are sputtered. In such cases a very strong magnet is used as some of the magnetic flux will be shunted into the magnetic material of the target. As the target is eroded the effective magnetic field at the front face of the target increases, which further accelerates the process. One complex method currently used in DC PVD processes is to use a position controlled magnet which is capable of moving location to more efficiently erode a larger area of the target. However, the tall spacing still results in an inefficient process as most of the sputtered material is deposited on the shields or collimator if utilized.
RF PVD process chambers also use a tall spacing and driving frequency of 13.56-27.12 Mhz operated in a pressure regime of 20-60 mTorr. The inclusion of RF can open the window to increase target utilization without sacrificing metal ionization. For example, metal ionization is higher for RF PVD than DC PVD processes. Electron confinement is enhanced and consequently gas ionization by the confinement of electrons due to stochastic heating from the oscillating field is predominantly in the Ez direction. This permits greater flexibility of the type of magnetron that can be used. For example, the magnetron track in an RF PVD system does not need to be closed, unlike a DC PVD magnetron which does need to be closed. In addition, the RF PVD magnetron can be larger than the DC PVD magnetron and still achieve high metal ionization levels at the wafer.
However at 190 mm spacing the inventors have observed that in order to achieve good deposition uniformity, the magnetic field must be predominantly produced at the target edge. This poses an issue in that the target is predominantly eroded at the target edge and as mentioned previously with magnetic materials this effect is pronounced.
Accordingly, the inventors have provided embodiments of improved substrate supports for use in substrate processing systems.